it's possible. that usually presents in a vibration at low speed. Just above idle and clears as the speed gets higher.
you could also have a problem with the dampner plate. But those are rare.
Are you comfortable shifting the trans at the trans? if so disconnect the cable and shift it firmly holding pressure while someone brings up the RPM. See what that does.

I have tried applying pressure to force the trans further while running (thinking the cone wasn't going far enough) - it didn't seem to change the vibration (I hadn't disconnected the cable so I was just pushing the springs on the cable farther)

I have tried applying pressure to force the trans further while running (thinking the cone wasn't going far enough) - it didn't seem to change the vibration (I hadn't disconnected the cable so I was just pushing the springs on the cable farther)

disconnect the cable and repeat. shift it at the normal idle speed and run the throttle up from there.

it can help rule out the shifter on the trans. You could also disconnect the drive shaft to the Sonic leg and see what happens. I doubt this will change anything because you won't be able to simulate a load.

Thanks to everyone who has helped out so far. Here is where the problem stands now:

Yesterday I tried to take apart the coupling between the transmission and the drive, however I found out that in order to get it apart that you need to remove the outdrive from the boat. (Why it is designed this way is beyond me!). Since I wasn't able to remove the coupling I put it back together and in doing so noticed that one of the bolts "may" have been loose.
Since I had taken things apart and put back together we ran the engine while at our mooring, in doing so we saw no shakes in either reverse or forward, so I thought I had fixed it. Today we took the boat out and ran up and down the ICW and found the problem was better, but not fixed. Now the vibrations start at 2800 RPM and are still there at 30000 while in forward (we didn't dare go any higher due to the sever shaking). In reverse things are better than they ever have been - no shakes seen right up to 3300 RPM. So I seem to have removed the vibrations at the lower RPMs, but not the higher RPMs, which incidentally are the RPM we normally run at!

Over several trials of moving the RPM from idle to max, once it did not vibrate at all (fluke?), ever other time it did except when manual pressure was applied to the shift lever on the transmission (right at the transmission) pressing it "farther" into forward (it didn't move, just pressure). When the pressure was applied at the beginning of the trial all the way up to 3000 rpm the vibration did not occur - this was consistent every time we tried it. If pressure was applied to the shift lever once the shacking started it had no effect.

When the engine is shaking, looking at the coupling (see photos below) between the transmission an the outdirve the major movement is on the transmission/engine side.

When the engine is shaking looking at the outdrive it is moving but only slightly (looks like the shake comes from the engine, but I can't be sure)

Of the suggestions see in previous posts:
- I have ruled out a bad Injector, as nothing is seen with transmission in neutral while running engine from Idle upto 3000 RPM.
- Have not been unable to check the bolt that Bradley mentioned. (Need to haul boat out)
- Have not been able to disconnect the transmission from the drive, to isolate transmission from drive (Need to haul boat out)
- Transmission cone has been ruled out as nothing seen at Low RPM and I don't think things are slipping.

Pat - I think we have done what you mentioned - What are your thoughts ?
<quote>
you could also have a problem with the dampner plate. But those are rare.
Are you comfortable shifting the trans at the trans? if so disconnect the cable and shift it firmly holding pressure while someone brings up the RPM. See what that does.<quote>

I planning on taking a closer look at the coupling between the transmission and outdrive to see if it looks out of alignment, as something did change there.

I really don't want to haul the boat until I'm pretty confident as to where the problem is - Any other suggestions Ideas ?
Thanks again for all the help.

Transmission/Outdrive Coupling:
Note: this is not bolted back together in this picture

Have you checked to ensure your motor mounts are solid and tight? We had a similar sounding problem with a relatively new Yanmar in the late 80's and the problem proved to be a broken motor mount that allowed the rear starboard side of the engine to lift up and begin to vibrate at certain rpm's.

FWIW...

s/v HyLyte

__________________"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."

You do not need to haul out to take off the coupler. Just unloosen the bolts holding the coupler, then pry the engine forward. There should be just enough play to let the coupler drop out. Otherwise you will need to remove the 8 lag screws holding the motor mounts and then slide the engine forward. This is a lot less work than removing and reinstalling the leg and the mounting bracket.

Also, with this method you will be able to check and adjust the engine and transmission alignment with the leg unit. If you remove the leg unit, you will have no way to check the alignment.

It doesn't look like you have followed Pat's instructions fully. Did you disconnect the shift cable at the transmission and use the small lever on the side of the actual transmission to shift the transmission directly?
This eliminates any mis-adjustment of the shift cable and confirms that the transmission is fully shifted into the forward gear. It is possible that the cable can prevent the cone clutch from engagin fully, particulrly if the detent on the shift mechanism of the transmission is weakened through use.

Robert

__________________
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the memories of a man in his old age, are the dreams of a man in his prime
Pink Floyd - 'Free Four'

Pat,
I'm comfortable tearing into the transmission partially. From looking at the manual it looks like I don't have the tools to do all of it, but if needed I could get part way then take it to a mechanic that does Or go pick up the tools (pullers). I did find a copy online here, but what is interesting is that it doesn't completely match the copy I have which is part of the main repair manual for the engine (the shift levers are on opposite sides, but it is listing the model # as the same as in my paper manual (which does match my transmission...)

What are your thoughts on a possible problem ?

HyLyte,
I checked all the mounts - the rubber is fine. I checked them all before posting here - I did find one that was loose and tightened it but this didn't change anything (It was the Forward bolt on the Fwd Port mount). I will check them again when the engine is vibrating just to be sure...

Robert,
The springs in the assembly were not pulled to their full extent when I was pushing on the lever, so I didn't feel that I needed to disconnect the cable as I didn't see what it would change.

Bradley,
I think your prout has a different coupler - on ours we need to have enough space to remove the bolt completely and the bolts are about 2 inches long. (I've tried putting a photo below as it doesn't seem to have worked in my last post... if not here is a link : photo )
I will look into shifting the engine by removing the engine mount bolts... (It is certainly better that the outdrive which is what sillette told me!).

Transmission/Outdrive Coupling:
Note: this is not bolted back together in this picture

Mark the side shifter plate so you can put it back exactly. It's designed to float around and be adjustable. Pull it off and look at the shift spur. See if there is excessive wear in the forward side. It can be flipped and reinstalled. I know it can on the KM2A. I think it can on the 3. If it's in good shape then it's probably a tear down to replace the drive cone.